Integrated circuit heat sink support and retention mechanism

ABSTRACT

The present invention provides an improved heat sink retention assembly, such that the heat sink is physically supported by a base rather than by an integrated circuit. Traditional heat sinks have an alignment feature that physically aligns and supports the heat sink by contact of the feature with an integrated circuit, and that transfers force applied to the heat sink to the integrated circuit. This transferred force may be seen as shear stress at the pins of integrated circuits such as pin-grid arrays, and may damage the integrity of the integrated circuit or its connection to an external circuit. The present invention provides alignment and support features remote from contact with the integrated circuit, and therefore provides support for the heat sink in a manner that does not place substantial stress on the integrated circuit.

This application is a divisional of U.S. Ser. No. 09/419,964, filed Oct.18, 1999, pending.

FIELD OF THE INVENTION

The invention relates generally to the mechanics of integrated circuitheat sinks, and more specifically to a heat sink mounting mechanism.

BACKGROUND OF THE INVENTION

Integrated circuits that perform complex tasks or deal with largevolumes of data, such as modem microprocessors and digital signalprocessors, often require as many as several hundred electricalconnections to external circuitry. These connections may includeinterfaces to system memory, cache, system buses, and a variety of othercontrol or support circuitry. Packaging integrated circuits such thatthey can be easily and reliably connected to an external circuitrequires a mechanism capable of making this large number of requiredelectrical connections in a manner that is secure and electricallyreliable. Furthermore, the large amount of heat produced by many suchintegrated circuits must be dissipated, and therefore must be accountedfor in designing the integrated circuit mounting and packaging systems.

One solution to the demand for a large number of interconnects is thePin-Grid Array (PGA), which is an array of pins spaced closely togetherextending from a surface of an integrated circuit package. The pins arespaced in a predetermined and standardized way such that they willcorrespond to sockets that have been designed to be compatible with theselected pin configuration. PGA integrated circuits are currentlyavailable with up to several hundred pins on a single package, and aretherefore widely used in industry for applications such as processorpackaging.

To dissipate heat generated by the PGA integrated circuit, a heat sinkis often applied to the side of the integrated circuit opposite the sidefrom which the electrical pin connections are mounted, such that theheat sink is oriented extending away from the printed circuit board towhich the integrated circuit is mounted. Such heat sinks are oftenconnected to the integrated circuit package by means of a spring clip, abar clip, or other clip mechanism that secures the heat sink on top ofand in secure physical contact with the integrated circuit. In someapplications, a thermally conductive material is applied between thesurfaces of the heat sink and the integrated circuit, to further ensurea good thermal connection between the two devices. Such mountingmechanisms have proven effective for mounting heat sinks to manydevices, in part because the low mass of the heat sinks used has alloweduse of clips and other retention mechanisms that produced littlephysical force on the integrated circuit.

But, as integrated circuits increase in complexity, they become moredifficult to mount and heat sink adequately. Faster integrated circuitswith more dense internal circuitry produce more heat over a givenphysical area than previous generations of integrated circuits. Also,the greater amount of circuitry on more dense integrated circuits mayrequire heat sinks that are physically larger than the top surface ofthe integrated circuit, or that have other larger or more complexgeometries.

Large heat sinks capable of dissipating many tens of watts of powerconverted to heat by such integrated circuits may cause unacceptableforces on the integrated circuits when mounted directly to theintegrated circuit package. For example, such systems may be required towithstand physical shock of up to 50 g, or 50 times the acceleration ofgravity, without undue physical stress. When this type of physical shockis applied to a processor with a very heavy heat sink attached to it,the weight of the heat sink can cause undue stress on the electricalconnection pins of the integrated circuit, such as shear stress. Also,the clips used to hold the heat sink on to the integrated circuit maynot be able to retain a very heavy heat sink under such heavyacceleration, and so may fail to acceptably secure heavy heat sinks.

Therefore, a device is needed to better support heavy heat sinks asapplied to integrated circuitry such as a PGA mounted integratedcircuit. Such a device should transfer the forces presented by the heavyheat sink under heavy acceleration away from the integrated circuit andonto a supporting structure such as a motherboard or securely mountedintegrated circuit socket.

SUMMARY OF THE INVENTION

A heat sink assembly is provided that has a heat sink alignment featurelocated thereon and that is remote from an integrated circuit contactarea of the heat sink. A heat sink support supports and aligns the heatsink in contact with the integrated circuit and mates with the heat sinkalignment feature of the heat sink. The heat sink support is mounted toa base, such that force applied to the heat sink is transferred to theheat sink support and to the base.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an integrated circuit and socket with an attached heatsink, consistent with the prior art.

FIG. 2 shows a detailed view of a portion of the integrated circuit andheat sink assembly of FIG. 1, consistent with the prior art.

FIG. 3 shows a PGA integrated circuit mounted on an improved socketassembly with a heat sink attached thereto, consistent with anembodiment of the present invention.

FIG. 4 shows an integrated circuit and socket with adjacent retentionmechanism elements that support and align a heat sink, consistent withan embodiment of the present invention.

FIG. 5 shows an integrated circuit and socket with retention mechanismelements that support and align a heat sink and that furtherincorporates heat sink retention clips and retention mechanism springs,consistent with an embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description of sample embodiments of theinvention, reference is made to the accompanying drawings which form apart hereof, and in which is shown by way of illustration specificsample embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that logical, mechanical,electrical, and other changes may be made without departing from thespirit or scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the invention is defined only by the appended claims.

Because of the increased size and weight of heat sinks needed todissipate the large amount of heat generated by integrated circuits asdiscussed above, a better method of mounting heat sinks to theseintegrated circuits is needed. Specifically, an apparatus is needed thatprovides for distributing the forces of a large heat sink under heavyacceleration to a mechanically stable mounting apparatus rather than tothe pins of the integrated circuit. The present invention provides suchan apparatus, and distributes these forces to the base of the integratedcircuit mounting socket and to the motherboard.

The present invention provides a mounting apparatus for a heat sink, tobe aligned with and supported in contact with an integrated circuit. Theheat sink is mounted to and supported by an integrated circuit socket orother external retention mechanism, and is positioned such that the heatsink is also in physical contact with the top surface of the integratedcircuit. The heat sink support and heat sink are designed such that thesupport bears a substantial portion of the dynamic forces of the heatsink under acceleration or force, thereby protecting the integratedcircuit from bearing these forces.

FIG. 1 shows a heat sink mounted to an integrated circuit and a socketin a manner that is typical of the prior art. A printed circuit board101 has attached to it a socket 102, capable of receiving andelectronically connecting with an integrated circuit. A heat sink 104 isattached to the integrated circuit 103 by a mounting clip 105. The clip105 is attached to the socket by affixing the clip to tabs 106 and 107,and applies physical pressure to the heat sink 104, the integratedcircuit 103 and the socket 102. The heat sink comprises in part one ormore ridges 108 that align the heat sink 104 with the integrated circuit103 when mounting the heat sink.

FIG. 2 shows an enlarged detail view of a ridge 201 that isrepresentative of ridges 108. The ridge 201 here is in physical contactwith the integrated circuit 202, and so both positions the heat sink 201relative to integrated circuit 202 and physically couples the heat sinkto the side of the integrated circuit. Because the heat sink isphysically constrained by edges of the integrated circuit that are incontact with the heat sink or heat sink ridges 201, any forces appliedto the heat sink will be transmitted to the integrated circuit 202. Forexample, when the heat sink undergoes heavy acceleration such as when acomputer containing such an assembly is dropped, the force of the heatsink upon rapid deceleration while stopping is applied directly to theintegrated circuit. This force may be borne as shear stress on theintegrated circuit pins that connect the integrated circuit to thesocket 203 in a device such as a PGA integrated circuit, and on theexternal body of the integrated circuit itself. As larger and heavierheat sinks become necessary to dissipate larger amounts of heat producedby advanced integrated circuits, these forces become unacceptably high,requiring a new means of mounting a heat sink to prevent transmission ofsuch heavy forces to the integrated circuit.

FIG. 3 shows an embodiment of the invention that provides offloading ofsuch forces from the heat sink directly to the socket, greatly reducingthe stresses applied to the integrated circuit. A socket 301 receivesthe integrated circuit 302, and electrically and physically connects theintegrated circuit to a printed circuit board 303. A heat sink 304 ismounted in contact with the top surface of the integrated circuit 302,and provides thermal cooling to the integrated circuit. The socket 301has one or more ridges such as ridge 305, designed to support the heatsink 304. The heat sink 304 has a corresponding slot 306 that mates withthe socket ridge 305 upon mounting of the heat sink, such that thephysical connection between the ridge 305 and the slot 306 physicallypositions and supports the load of the heat sink. The heat sink is againattached to the socket by a clip, which extends over the heat sink andis attached to tabs 307.

Such an apparatus must be designed with a specific geometry, so that theheat sink 304 contacts the integrated circuit 302 when it is supportedby the socket such as by ridge 305 and slot 306. Although the socket 301supports the heat sink 304 in this embodiment, the heat sink 304 mustremain in physical contact with the integrated circuit 302 to providethe intended cooling effect. Thermally conductive material may beapplied between the heat sink 304 and the integrated circuit 302 to fillany voids and allow less strict tolerances in designing the assembly.But, even use of a thermally conductive paste cannot compensate forlarge variations in assembly geometry, and a design such as thisembodiment of the invention must be designed so that the heat sinkcontacts both the integrated circuit and is supported by the socket.

In another embodiment of the invention, a heat sink retention mechanismallows use of a standard socket, and also supports the heat sink in amanner that does not apply stress to the integrated circuit when theheat sink is under force. A standard socket 401 is provided, that iscapable of receiving an integrated circuit 402. The socketelectronically and physically connects the integrated circuit to aprinted circuit board 403. A heat sink 404 is positioned in physicalcontact with the integrated circuit 402, and provides cooling to theintegrated circuit by dissipating heat. A retention mechanism comprisingelements 405 and 406 is mounted on the printed circuit board 403 in aposition adjacent to the socket 401, and is securely mechanically fixedto the printed circuit board.

After the integrated circuit 402 has been mounted in the socket 401 andthe retention mechanism 405 and 406 is securely fixed to the printedcircuit board 403, the heat sink 404 is mounted in contact withintegrated circuit 402 and retained by retention mechanism 405. Force onthe heat sink is therefore applied to the retention mechanism ratherthan to the integrated circuit, thereby reducing the shear stress on thepins of the integrated circuit and other potentially damaging forces. Anexternal retention mechanism such as in this embodiment is advantageousin that it can support very large heat sinks, because the size of theheat sink need not correspond to the integrated circuit or its socket,but is supported instead by an external retention mechanism.

In one further embodiment of this invention, the retention mechanism 405and 406 is affixed to the printed circuit board by mounting pins 407that interface with mounting holes 408 in the printed circuit board. Theretention mechanism also comprises one or more attachment mechanismssuch as clips 409. The heat sink is attached to the retention mechanismby attachment mechanisms 409, and is physically supported by theretention mechanism such that it is in contact with integrated circuit402. The components of such an embodiment must be of a geometry that isspecifically designed to support the heat sink such that it is inphysical contact with the integrated circuit, ensuring efficienttransfer of thermal energy from the integrated circuit to the heat sink.Thermally conductive material commonly known as heat sink grease mayagain be applied to the interface between the heat sink 404 and theintegrated circuit to provide a more thermally efficient connection, butcannot compensate for large variances in geometry of the components ofsuch an embodiment.

FIG. 5 illustrates an alternate embodiment of the invention that allowsuse of a standard socket via a retention mechanism as in FIG. 4, butfurther incorporates flexible retention clips 501 to hold the heat sinkin place. A standard integrated circuit socket 502 is electronically andphysically connected to the circuit board 503. The socket receives anintegrated circuit 504, and physically and electrically connects theintegrated circuit to the circuit board 503. A heat sink 505 ispositioned in physical contact with the integrated circuit 504, and insome embodiments further incorporates a fan 506 to provide forced airflow to further assist in cooling. Retention mechanism elements 507 arephysically mounted to the circuit board 503 in a position adjacent tothe socket 502 such that they can receive and hold the heat sink 505 ina proper position relative to the integrated circuit 504.

Mounting pins 508 affix the retention mechanism 507 to the circuit board503 by mating with mounting holes 509 in the circuit board. Flexibleretention clips 501 have openings 510 therein, which clip onto tabs 511of the retention mechanism elements. The retention clips also have anopening 512 that captures but does not clip onto tab 513 of theretention mechanism elements, thereby limiting the displacement betweenthe assembled heat sink 505 and integrated circuit 504 under shock orforce.

The embodiment of FIG. 5 when assembled cradles the heat sink 505 in theretention mechanism elements 507 such that the flat bottom surface ofthe heat sink assembly contacts the flat top surface of the integratedcircuit 504. Thermally conductive material such as heat sink grease maybe applied to the contact surface to ensure an efficient thermalconnection. A retention mechanism spring 514 in some embodiments furthersupports the heat sink, but does not exert sufficient pressure on theheat sink to prevent it from resting in contact with the integratedcircuit.

Retention clips 501 hold the heat sink assembly in the retentionmechanism elements when assembled, and provide a spring force thatpushes the heat sink assembly into the retention mechanism elements. Theretention clips further restrict the amount by which the heat sinkassembly may move against the spring force provided by the clips viaretention clip opening 512 and tab 513. The opening 512 is larger thanthe tab 513 and does not contact the tab, except to prevent furtherflexing of the flexible retention clip when the heat sink is under forceand has flexed the retention clip far enough to reach a desired heatsink displacement limit. Therefore, the heat sink retention mechanism ofFIG. 5 not only supports the heat sink in a way that does not transferforce from the heat sink to the integrated circuit, but provides springloading of some heat sink forces to further reduce the force transferredto the circuit board or integrated circuit when the heat sink is underhigh acceleration, such as when dropped.

The example embodiments of FIGS. 3, 4 and 5 are examples of heat sinkmounting mechanisms that support and position the heat sink in contactwith the integrated circuit, but that do not transfer force from theheat sink to the integrated circuit. The invention includes theseexamples and other embodiments with mating features on a heat sink orheat sink support such that a mating feature or combination of matingfeatures supports and aligns the heat sink. The heat sink matingfeatures improve upon the prior art alignment or mating features in thatthey do not contact or apply force to the integrated circuit, but areremote from the area at which the integrated circuit and heat sink arein contact. The invention offers an improvement over the prior art inthat it provides mounting of a heat sink to cool an integrated circuitin such a manner that the integrated circuit does not bear substantialshear stress from the heat sink when a force on the heat sink causes theheat sink to apply force to its mounting, such as under heavyacceleration.

A variety of other embodiments of the invention exist, and need notspecifically include a retention mechanism as shown in FIGS. 4 or 5, ora ridge 305 and slot 306 as pictured in the embodiment shown in FIG. 3.It is specifically contemplated that other mechanisms exist that maysatisfactorily support a heat sink and that physically couple the heatsink to a base such as a printed circuit board withoutphysically-coupling the heat sink to the integrated circuit. Theseembodiments of the invention improve over the prior art in that the heatsink of the embodiments does not apply substantial stress to theintegrated circuit when under force.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations of the invention. It isintended that this invention be limited only by the claims, and the fullscope of equivalents thereof.

We claim:
 1. An integrated circuit socket, comprising a plurality ofdistinct mating features that mate with a plurality of distinct matingfeatures of a heat sink such that the integrated circuit socket and heatsink when mated are configured to contain an integrated circuit, andsuch that the mating features of the integrated circuit socket align andsupport the heat sink and offload forces from the heat sink to theintegrated circuit socket, reducing stress applied to the integratedcircuit when the heat sink is under force toward the integrated circuit.2. The integrated circuit socket of claim 1, wherein the at least one ofthe mating features of the heat sink comprises a slot.
 3. The integratedcircuit socket of claim 1, wherein at least one of the mating featuresof the integrated circuit socket comprises a ridge.
 4. The integratedcircuit socket of claim 1, wherein the heat sink is attached to theintegrated circuit socket by one or more clips.
 5. The integratedcircuit socket of claim 4, wherein the one or more clips have one ormore openings therein that are captured by and are larger than tabs onthe integrated circuit socket, such that the tabs do not contact the oneor more clips except when the one or more clips have flexed to a desiredheat sink displacement limit.
 6. A heat sink support that supports andaligns a heat sink, comprising: a socket with a plurality of distinctmating features that mate with a plurality of distinct mating featuresof the heat sink such that the mating features support and align theheat sink remote from an integrated circuit contact area and such thatthe socket and heat sink contain an integrated circuit when the socketand heat sink are mated, such that the socket offloads forces from theheat sink to the socket, reducing stress applied to an integratedcircuit when the heat sink is under force toward the integrated circuit.7. The heat sink support of claim 6, wherein the at least one of themating features of the heat sink comprises a slot.
 8. The heat sinksupport of claim 6, wherein at least one of the mating features of thesocket comprises a ridge.
 9. The heat sink support of claim 6, whereinthe heat sink is attached to the socket by one or more clips.
 10. Theheat sink support of claim 9, wherein the one or more clips have one ormore openings therein that are captured by and are larger than tabs onthe socket, such that the tabs do not contact the one or more clipsexcept when the one or more clips have flexed to a desired heat sinkdisplacement limit.